Centrifugal pumps are a general-purpose fluid machine widely used in chemical pump industrial systems. It has a wide range of performance (including flow, pressure head and adaptability to the nature of the transport medium), small size, simple structure, easy operation, low operating costs and many other advantages. Usually, the flow rate and pressure head of the selected centrifugal pump may be inconsistent with the requirements in the pipeline, or due to changes in production tasks and process requirements.
At this time, the flow adjustment of the pump is required, which essentially changes the working point of the centrifugal pump. The working point of the centrifugal pump is determined by the characteristic curve of the pump and the characteristic curve of the piping system. Therefore, changing the characteristic curve of any one can achieve the purpose of flow regulation. At present, the flow regulating mode of the centrifugal pump mainly includes the regulating valve control, the shift control, and the parallel and series adjustment of the pump. Due to the different principles of various adjustment methods, they have their own advantages and disadvantages.
1. Change the pipeline characteristic curve
The simplest way to change the flow rate of the centrifugal pump is to use the opening degree of the pump outlet valve to control. The essence is to change the position of the pipeline characteristic curve to change the working point of the pump.
2. Change the centrifugal pump characteristic curve
According to the law of proportionality and cutting law, change the speed of the pump, change the pump structure (such as the cutting impeller outer diameter method, etc.) two methods can change the characteristic curve of the centrifugal pump, so as to achieve the adjustment of flow (and change The purpose of the indenter). However, for the pump that has been operated, the method of changing the structure of the pump is not convenient, and the versatility of the pump is reduced due to the change of the structure of the pump, although it is economical to adjust the flow rate at some time, and is also very good in production. Less adopted. Here, only the method of changing the rotational speed of the centrifugal pump to adjust the flow rate is analyzed. From the analysis in Figure 1, when changing the pump speed regulation flow from Q1 to Q2, the pump speed (or motor speed) drops from n1 to n2, the pump characteristic curve QH and the pipeline characteristic curve He=H0G1Qe2 at the speed of n2 (The pipeline curve does not change) at point A3 (Q2, H3), point A3 is the new operating point after the flow rate is adjusted by the speed regulation. The adjustment method is obvious, fast, safe and reliable, which can prolong the service life of the pump and save energy. In addition, the speed operation can also effectively reduce the NPSHr of the centrifugal pump, keep the pump away from the cavitation zone, and reduce the centrifugal pump. The possibility of cavitation [2]. The disadvantage is that changing the speed of the pump requires changing the speed of the prime mover (usually the motor) through frequency conversion technology, the principle is complicated, the investment is large, and the flow adjustment range is small.
3. Pump seires connection and parallel adjustment mode
When a single centrifugal pump can not meet the delivery task, you can use the parallel or series operation of the centrifugal pump. Two parallel pumps of the same type are used in parallel. Although the head change is not large, the total delivery flow is increased. The total efficiency of the parallel pump is the same as that of a single pump; when the centrifugal pump is connected in series, the total head is increased. The flow rate does not change much, and the total efficiency of the series pump is the same as that of a single pump.
